Not Applicable.
The present invention relates generally to a method for forming a flowline and, more particularly, to a method of directional boring a trenchless flowline bore using sight relief holes to set the proper grade and line and to prevent the pressure from building up about the pipe as it is placed within the flowline bore.
Proper installation of underground utilities such as storm sewer and sanitary sewer lines require boring a linear Bowline. It is desirable, and oftentimes mandatory, to install the flowline at a constant grade from one end of the flowline to the other. Ideally, once the flowline is completed, a lamp is shown at one end of the line. If the lamp is completely visible at the opposing end of the flowline, then a substantially constant grade has been maintained along the length of the flowline, and the flowline will effectively drain in the proper direction.
In the past, a number of methods have been used to install pipes with flowlines. The primary method of construction is open digging or trenching. To dig a flowline, a large trench is dug along the entire length of the line. Typically, a trench box is placed within the trench to protect workers located within the trench. The box is moved incrementally along the path of the flowline installation as the flowline is being built. Gravel and earth are placed around the pipe to maintain the location of the pipe, and the trench is subsequently back filled after the trench box is moved down the path of the flowline installation.
The open digging process suffers from a number of significant drawbacks. For instance, open trenches are hazardous for workers open digging the trench. It is possible for equipment and other objects to fall into the trench and strike workers therein. Also, it is common for large sections or clods of earth to dislodge and tumble into the open portions of the trench not protected by the trench box. Since soil typically weighs more than 100 pounds per cubic foot, even a small section may cause serious injury or death, particularly at the depths at which many flowlines are installed. Likewise, open trenches present an obvious danger to children and other bystanders.
The sheer size of the trench required for open digging also causes a number of problems. A great deal of time and effort is devoted to both digging and refilling each trench. Also, many digging locations, such as urban environments, simply do not have convenient locations at which the trenches may be dug. Additionally, the excess trench materials must be hauled away at the expense of the contractor or owner of the utility being installed.
Many other problems are associated with the open digging process. For instance, restoration of the site to its condition prior to installation of the flowline is difficult. It is particularly difficult to restore the continuity of the pavement and other ground conditions at the installation site. Also, the costs are substantial to fill around the pipe with granular backfill to keep the pipe in place. Other problems include the difficulties associated with digging under inclement weather conditions, the negative environmental impact of the open digging process, expensive removal of water from the ground prior to digging, and the high fuel costs of operating open digging equipment.
Additionally, the impact on businesses and the local economy, environment and quality of life is great. Taking all of these negatives into consideration, other methods such as tunneling and auger boring are sometimes utilized for flowline installations. To install a flowline by tunneling, large pits are dug at the entrance and exit points, and the installing machine is located within the entrance pit. The machines may be operated either within the confines of the machine or remotely at the surface. In the tunneling method, the pipe is jacked into place within the bore by hydraulic rams as the tunneling equipment is used to cut the soil. At the end of the installation, the tunneling equipment is detached from the pipe and removed from the exit pit.
While the tunneling process overcomes some of the problems associated with open trenching, it too suffers from significant drawbacks. Since the tunneling equipment required to install smaller diameter bores is complex and expensive, it is uncommon for tunneling to be used for bores of less than three feet in diameter, and oftentimes cost prohibitive for bores having a diameter of less than two feet. Also, tunneling equipment is bulky and heavy, and cranes are commonly needed to lower the equipment into place. Moreover, a significant area must be set aside above ground for placement of the equipment used to guide the tunneling machine and recycle fluids during the tunneling process. Also, in the tunneling process, the pipe must have sufficient strength to withstand the forces of the hydraulic jacks. Steel and other pipe materials that have the strength to withstand these forces are susceptible to corrosion if used in acidic soil conditions, or as sewage or storm water drains. Thus, it is sometimes necessary to place a carrier pipe within the pipe installed by the tunneling method. This adds expense both during installation and maintenance of the flowline.
As mentioned above, auger boring has also been used as an alternative to open digging. Similar to the tunneling process, entrance and exit pits are dug at the endpoints of the desired line, and an auger machine is set into place within one of the pits. A cutting head is fastened to a length (or flight) of augers, and the augers are shoved through the pipe that is to be installed. Additional auger flights are added to the machine and pushed forward using a jacking process. as the bore is formed, the material from the bore hole is removed by the screw-like augers.
The most significant drawback to auger boring is the lack of guidance. Extreme care must be taken prior to setting up the auger boring machine to ensure that the machine is at the proper grade and line. In the auger boring process, a carrier pipe is required for two reasons. First, the pipe is located within the bore by a jacking process similar to tunneling, and must withstand the jacking forces. Secondly, the grade and line of the auger bore are oftentimes incorrect, and the carrier pipe is installed within the outer pipe to meet the required grade. In addition to these problems, installations of significant lengths require expert operators and are difficult to complete in a timely and consistent manner.
To address the problems of the aforementioned methods, directional drilling machines, such as those sold under the tradenames DITCHWITCH, VERMEER and CASE have been developed to directionally drill flowlines. A drilling machine is placed on the surface at a distance from the desired starting location of the bore. Downhole tooling is attached to a drill stem and drilled through the ground along a pilot hole from the surface of the ground to the desired starting location, and then along the path of the desired flowline. Additional sections of drill rods are added to the drill stem as the pilot hole is made. Electronic tracking components are disposed on the machine and downhole tool to guide the downhole tooling as the pilot hole is drilled. Once the pilot hole is complete, a hole opener such as a reaming head is placed on the machine and the pilot hole is backreamed to create the desired bore while the pipe is being pulled into place.
While the use of directional drilling machines eliminates many of the problems associated with open trenching, the machines also suffer some serious drawbacks. Namely, the electronic tracking components are not accurate enough to install the bores at the line and grade required for flowline bores. Thus, directional drilling machines are usually utilized for utilities that do not require very accurate line and grade, such as phones cables and pressure systems. Prior attempts to drill bores that require specific lines and grades are few, and the success rate has not been high. With current methods, when the flowline is drilled at a significant depth and/or the grade is relatively slight, the electronic tracking components simply can not control the tooling with the required precision.
Also, in the process currently used for directional boring, the dirt slurry remaining in the bore after the back reaming process is not always entirely pushed out of the ends of bore as the pipe is pulled into the bore. Consequently, a great deal of pressure is developed between the outer surface of the pipe and the bore sidewalls. This pressure can cause the pipe to collapse, pull apart or deflect from the intended line and grade. If the bore size is increased with respect to the diameter of the pipe to minimize pressure build-up, the pipe can float or deflect with respect to the desired centerline of bore, and the desired grade of the flowline pipe will not be achieved. When floating or deflection occurs, the flowline bore is quite likely to fail the lamping test, have high and low spots, and will not satisfy the requirements specified in the codes for proper installation of flowlines as dictated by local laws.
The present invention is an improved method of installing a flowline below the surface utilizing directional boring. The method includes the steps of establishing first and second site relief holes along a linear path, positioning a directional drilling machine on the surface, boring a first portion of a pilot hole from the surface to the first sight relief hole, determining the elevation of the boring tool and adjusting the boring tool to the desired elevation, boring a second portion of the pilot hole to the second relief hole, and determining the elevation of the boring tool and adjusting the tool to the desired elevation.
In another aspect of the invention, a method for directionally boring a flowline is provided. The method includes the steps of establishing a number of sight relief holes along the desired path of the bore, directionally drilling a pilot hole, reaming the material around pilot hole to define a bore wherein a portion of the bore is filled with a slurry of the reamed material, and pulling a pipe into the bore wherein a portion of the slurry is displaced into the site relief holes so that pressure does not develop around the pipe.
By providing the methods in accordance with the present invention, numerous advantages are achieved. For instance, flowlines may be located with great accuracy, and at depths at which machines have been unsuitable heretofore. The disturbance at the construction site is lessened since fewer and smaller excavations are needed, and significantly less surface area is needed for the equipment. Moreover, less fuel is consumed in the methods of the present invention, and the overall social costs are reduced. Of great import, the working conditions are much safer for both workers and bystanders because of the reduction and near elimination of open excavation. The sight relief holes prevent pressure from building around the pipes to allow the flowline bore to be drilled at a diameter only slightly greater than the diameter of the pipe. This allows the pipe to be pulled in place accurately within the bore. Thus, the problems of pipe float or deflection can be avoided, and pipes may be placed at great depths and at very slight grades.